From the beginning, the creators of Washington, D.C., went to some trouble to conceal that their capital was built on shaky ground.

On October 17th, during a speech on ethics reform, Donald Trump announced, “It is time to drain the swamp in Washington, D.C.” A day later, he repeated the phrase in a tweet, adding the hashtag #draintheswamp for good measure. It was late in the campaign for a new slogan, but soon audiences were chanting it.

Trump’s use of the phrase was not the first. Ronald Reagan was fond of it back in the nineteen-eighties, and decades earlier, at the opposite end of the political spectrum, socialists had also sought to “drain the swamp”—of capitalism. Trump himself was wary of the locution at first. At a rally in Des Moines, he told the story:

Funny how that term caught on, isn't it? . . . I tell everyone, I hated it. Somebody said “Drain the swamp,” and I said, “Oh, that is so hokey. That is so terrible.” . . . I said, all right, I'll try it. . . . So, like a month ago, I said, “Drain the swamp,” and the place went crazy. And I said, “Whoa, what's this?” Then I said it again. And then I start saying it like I meant it, right? And then I said it—I started loving it, and the place loved it. Drain the swamp. It's true. It's true. Drain the swamp.

There are moments in a hard-fought campaign when a catchy cluster of words can suddenly bubble up from the depths, a shiny new lily pad. “Drain the swamp” worked on many levels—it was active, it was funny, and it sounded like something a man in the real-estate business would actually say. It offered no details—another plus—and held a folksy charm.

It was also historically accurate. Indeed, the candidate had landed on a point the Founders had gone to some trouble to conceal—that the foundation upon which they built their capital included a great deal of water, sand, and mud.

The swamp in question has never been easy to drain, or, for that matter, even to locate. From its founding, on not very solid ground, Washington, D.C. has been terraqueous; a city of both land and water, where maps chart realty and reality interchangeably.

The federal district came into existence as little more than a doodle, after it was decided, in the summer of 1790, to build a new capital upon the banks of the Potomac River. Despite the isolation of the location, many miles upstream from Chesapeake Bay, ambitions were high.

A scrap of paper in the Library of Congress, from around March, 1791, shows the earliest appearance of the plan. With a few quick strokes of his pen, Thomas Jefferson outlined a master vision: the single word “President” above the future location of the White House, and another word, “Capitol,” to the east. In between, there would be “public walks,” which was an accurate description of the Mall to come.

Jefferson was channelling the ancients as he daydreamed of the future. Over a small stream, he sketched the word “Tyber,” after Rome’s river. A nearby elevation called Jenkins Hill would soon be renamed Capitol Hill, after Rome’s Capitoline. Soon, elaborate street plans, with parks, grids, and slashing diagonals resembling those of Versailles, would be traced over a terrain that still housed more bears than people.

Progress came slowly, as the land in question refused to coöperate. Pierre Charles L’Enfant, the brilliant French draftsman hired to work out the details, complained that the land was “swampy.” In Jefferson’s sketch, there are signs of the trouble to come: low soundings for the shallow Potomac and a “Mud Bank” not far away from the federal city. The water was often brackish; a few years earlier, in 1785, George Washington had written a letter praising the Potomac for precisely this reason (“the bed of the Potomac before my door, contains an inexhaustable fund of manure”). That was helpful to farmers, but less so to government employees.

Why did the Founders choose such a remote place for their capital? That, too, was a bit of a swamp. When George Washington was inaugurated, in April, 1789, New York was the seat of government—the latest in a long list of places where Congress had met, including Philadelphia, Lancaster, York, Baltimore, Annapolis, Trenton, and Princeton. But the issue was festering, and so many proposals were still coming in, for Northern and Southern versions of the capital, that one satirist proposed a mobile platform, with a few buildings and a statue of George Washington, which could be wheeled from one location to another.

In the spring of 1790, Congress, already dysfunctional, argued over everything, and high on the list of disagreements were its permanent location and its ability to pay for itself. The two issues were eventually fused in a masterly compromise, struck by Jefferson, Madison, and Hamilton, around June 20th. In what may have been the most consequential dinner in American history, they met at Jefferson’s New York residence, at 57 Maiden Lane—the room where it happened, known to every “Hamilton” fan—to hammer out the details. On the table was the deal of deals. Congress would agree to assume the debt burden of the states, easing the creation of a strong economy, soon to be centered in nearby Wall Street. In return, Hamilton would agree to support the South’s dream of a capital closer to home.

Thomas Jefferson’s account of the dinner, in 1790, that led to the creation of Washington, D.C. MANUSCRIPT DIVISION, LIBRARY OF CONGRESS

MANUSCRIPT DIVISION, LIBRARY OF CONGRESS

Jefferson appeared to regret the arrangement; he confessed to George Washington that it was the worst political mistake of his life, because an invigorated economy had given rise to a “speculating phalanx” that had revealed, very early, the dispiriting influence of money in our politics. But Northerners, too, would question a deal that now required them to travel a great distance, along terrible roads, to a capital that seemed to be settling into the ooze it was built upon.

As it turned out, the “speculating phalanx” was active in the South, as well, where investors long before had bought land around the future site of Washington. A low-grade “Potomac fever” had coursed through the bloodstream of these investors, as they pursued a dream of luring settlers to the enchanted spot. They imagined a grand city of commerce arising from the manure-rich banks of the river.

Unfortunately, from a hard-nosed business point of view, the Potomac is one of the most disappointing rivers in North America, promising much but delivering almost nothing. It begins in the mountains of Virginia and West Virginia, and its waterfalls impede navigation. Seventeen miles of portage were required to travel upriver, toward Cumberland and Harpers Ferry. During much of the year, the river is too shallow for large vessels. To this day, it is remarkably shallow, despite efforts to dredge deeper channels.

One disappointment stung in particular. The backers of the new location hinted strongly of a distant connection to the Ohio River, the great natural conduit into the interior of North America, and ultimately to the Mississippi and the Gulf of Mexico. It would have been wonderful, if true. For generations, Virginian promoters had promised such a connection, and explorers wandered the forests of western Virginia and Pennsylvania to prove somehow that there was an easier way to reach the Ohio than there was. To Washington, Jefferson wrote, “Nature has then declared in favour of the Patowmac, and through that channel offers to pour into our lap the whole commerce of the Western World.”

It was a typically Jeffersonian thought; eloquent, ambitious, and insistent that a hoped-for truth was self-evident. But in the end, despite all the promises, the connection did not exist, as Thomas Jefferson knew very well (his father, Peter Jefferson, had surveyed the Potomac to its disappointing sources). Washington was built upon a foundation of hyperbole, a mud bank like the one Jefferson sketched into his map.

There was one industry that the new city would excel in, which did not require ships, portages, or much labor at all. An intense lobbying effort was launched in the crucial years of 1789 and 1790 by investors in the future site, claiming that the city would soon be larger than London, that children would regard it with "rapture," and that it would be “the only imperial city ever yet founded on the immutable and eternal principles of liberty and reason.” Compared to the extraordinary Potomac and its vast watershed, the Thames, Seine, Rhone, and Garonne were mere “rivulets.” Providence, they said, had ordained that the city should be built here, now.

So it happened—eased by the dinner deal, and by the extraordinary prestige of the figure whose name the new city would bear. Washington may be the only city on Earth that lobbied itself into existence.

From these muddy banks the capital grew, and on occasion it lived up to its billing. The Capitol was magnificent, as was the White House, and, as a permanent community began to settle there, Washington took on some of the attributes of a city—newspapers, banks, and a robust hospitality industry that specialized in giving temporary shelter to legislators. But over time it became clear that the new city’s brackishness was a problem. Simply put, there was too little water in the Potomac and too much of it on land. Congressmen disliked having to tiptoe around what they called “the swamps of Pennsylvania Avenue” to get to the White House. That avenue was nicknamed “the great Serbonian bog.”

Periodic attempts to build canals around the waterfalls brought slow-moving, stagnant, odoriferous waters that seemed to symbolize the inertia of government. The city that lacked a navigable river also suffered from a different problem: fetid creeks that carried raw sewage to and from its different population centers, which were far from one another (early visitors called it, facetiously, “the city of magnificent distances”). A Massachusetts congressman, Theodore Sedgwick, wrote, in 1789, “the climate of the Patowmack is not only unhealthy, but destructive to northern constitutions.” The smells of the District added fuel to the growing critique of a city that offended Northerners for its adherence to slavery as well as its inaccessibility. To an abolitionist like William Lloyd Garrison, Washington was a moral swamp: “The District is rotten with the plague, and stinks in the nostrils of the world . . . a fouler spot scarcely exists on earth.” An eyewitness in 1860 cast an eye on the city’s canals and glimpsed “dead cats and all kinds of putridity,” in a stagnant pool “reeking with pestilential odors.”

Fortunately, the capital could always rely on its genius for self-promotion when nature refused to coöperate. When General LaFayette visited in 1824, he happily complied with local custom by delivering a magnificent sound bite, and referring to the small, muddy town as “the central star of the constellation which enlightens the whole world.”

With time, the capital filled itself in. The “magnificent distances” began to make more sense, as tens of thousands moved there during the Civil War and its aftermath. That war’s legacies included a city that had become a genuine national capital, supported by a vastly enlarged government and military. Over the next century, Washingtonians shored up their infrastructure through land reclamation projects and other public works that took better advantage of the Potomac and its tributaries. The river would never become a major artery of commerce, but it was beautiful all the same, and by diverting water into new channels architects were able to construct the vistas we know and love so well, including the reflecting pool before the Lincoln Memorial and the tidal basin by the Jefferson Memorial.

A group of boys on the National Mall, in 1926. LIBRARY OF CONGRESS

LIBRARY OF CONGRESS

Still, there are occasional reminders of the swamp lurking just below the gleaming surfaces. Because Washington is located just below a waterfall, this bit of the Potomac will always be a busy meeting place of sea creatures, where saltwater fish sometimes swim in, very far from Chesapeake Bay, to mingle with their freshwater cousins. Sharks have been sighted within the waters of the District, as a natural history of 1918 confirmed. In September, 2015, an eight-foot bull shark was caught downriver, in St. Mary’s County.

Sometimes the waters demand attention more urgently. In 2006, the long-forgotten Tiber Creek reasserted itself, by rising up from its underground bed, where it still courses below Constitution Avenue, and threatening the actual Constitution of the United States. That document is preserved in a secure vault in the National Archives, along with the Declaration of Independence. After a severe rainstorm, the underground waters rose rapidly, stopping, fortunately, well short of the documents, but reaching alarming levels, coursing through the Archive’s basement and a theatre, where visitors could find an unwelcome reflecting pool the next day, lapping at their feet.

On January 20th, a new President will be sworn in, and the structure being created to accommodate the transfer of power is now complete. The temporary platform recently built below the West Front of the Capitol is painted white, to match the building behind it, and includes small touches that reflect the classical grandeur that the Founders sought. During the Inauguration, it will support the weight of hundreds of people, including the incoming and outgoing Presidents, their families, and their confidants.

It will also carry the weight of the world’s attention, as the television cameras beam their broadcasts from this spot around the world. In the exact place where Thomas Jefferson wrote the word “Capitol” on his 1791 sketch of the future city, the leaders of the United States will gather, once again, to contemplate the questions he raised in his own Inaugural, the first to be held there, in 1801. That address, following a bruising campaign, promised to unite all Americans “with one heart and one mind,” and to banish a “political intolerance” that was already, at that early date, dividing the nation. Looking out at the multitudes, Jefferson asked for their help to steer the ship of state across waters that were already roiled. He didn’t use the phrase “ship of state”; instead, he called it “the vessel in which we are all embarked amidst the conflicting elements of a troubled world.” Still, it was a nautical metaphor (Noah’s Ark springs to mind) and the roiled waters were real—not only in the sense that many Americans were having a hard time accepting the result of his election but because Jefferson’s “Tyber” was gurgling nearby, just down the hill from the sparkling new Capitol.

Those waters may not be self-evident, but they still flow, hidden from view. At noon on the 20th, a global audience of billions will see a familiar democratic ritual conducted, and a new time beginning, from this platform. But far below the Capitol, below even the tunnels that carry busy senators and representatives from one underground chamber to another, the waters of the Tiber will continue to murmur, a subterranean reminder of a swamp that has survived centuries of human attempts to eradicate it.

Ted Widmer edited “The New York Times Disunion: A History of the Civil War.”